This invention relates generally to temperature sensitive electrical circuits. Specifically, the present invention relates to a circuit which provides an output signal that reflects both an input signal and temperature. More specifically, the present invention provides a flexible system building block which may be inserted in a signal path when overall system performance can improve through temperature compensation of particular signals.
The performance of many circuits tends to change when the circuit's temperature changes. Automatic gain circuits and crystal controlled oscillators are two examples. This change in performance is often detrimental to overall system performance. Thus, a system design may include additional circuitry to compensate for the detrimental effects of temperature changes.
Although those skilled in the art use various temperature compensation schemes, such prior art schemes tend to use individual compensation circuits for each temperature compensation need. Conversely, the present invention provides a single temperature compensation building block which can be used in a variety of different ways to achieve many different compensation tasks.
A typical system design approach which incorporates temperature compensation would be to select and interconnect components that produce a desired result at room temperature, then repetatively review and modify the design to insure proper performance over a desired temperature range. Temperature compensation aspects of a design would not be considered until after the basic room temperature design has been completed. Accordingly, a temperature compensation building block that has no effect at room temperature yet provides compensation for more extreme temperatures would greatly aid system design efforts.
Temperature sensors may represent a prior art temperature compensation building block. One type of sensor known in the art utilizes the difference in voltage between the base and emitter junctions of transistors operating at different current densities to indicate temperature. However, such sensors merely provide an output voltage which varies as a function of absolute temperature and do not achieve temperature compensation without additional circuitry to combine the temperature signal with a signal that is to be temperature compensated. Additionally, such sensors require control over the resistance of on-chip resistors and over the area of transistor emitter junctions in order to control the responsiveness of the sensor to temperature. Furthermore, individual temperature compensation schemes which use such sensors must make allowances for the temperature characteristics of the additional components used in the combining circuitry.
The prior art temperature compensation building blocks, such as the sensor mentioned above, do not conveniently fit into the typical design process because they require a complicated and costly design effort for each individual temperature compensation task. For example, if an input signal needs temperature compensation a designer must discover how to combine a temperature sensitive signal from a temperature sensor with the input signal. The designer must further determine how to control the absolute temperature indicated by the sensor so that the temperature signal affects the input signal only to the amount that the temperature differs from room temperature. Furthermore, a temperature analysis must include the temperature characteristics of the components used in achieving the combining and controlling functions.
Accordingly, it is an object of the present invention to fill a need for reducing the complication and cost inherent in a temperature compensation design effort by providing a system building block that permits simple and easy to design temperature compensation.
Another object concerns flexibility so that the present invention can be useful for a wide variety of applications.
Still another object concerns providing a circuit that may be incorporated within integrated circuits, may be an integrated circuit by itself, or may be constructed using discrete components.